CONFUSION ON THE FLT DECK IN PROX OF TSTM ACTIVITY IN A NIGHT OP.

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NBOUND AT 33000 FT ON PUBLISHED ARR; GS 600 KTS PLUS WITH SMALL CELLS FIRST VISIBLE ON 80 MI RANGE. FOLLOWED THEM THROUGH 50 MI RANGE THEN 25 MI RANGE. CAPT FIRST NOTICED WX RETURNS AT 25 MI RANGE; SAID LATER THAT HE WAS NOT AWARE THAT SETTING HAD CHANGED TO 25 MI RANGE. CAPT TOLD ME TO REQUEST DEV; CTLR SAID UNABLE UNTIL YOU GET TO FL310; CLRED TO FL310. CAPT SAID AGAIN; WE NEED TO DEVIATE. BY THAT TIME LESS THAN 5 MI; 30 SECONDS TO CELL. I TOLD CTR WE HAD TO DEVIATE; COULD GO L OR R. CTLR SAID GO L. WHEN I THEN LOOKED UP FROM RADAR; CAPT WAS IN FULL 30 DEG R BANK. WITHOUT PREVIOUSLY ANNOUNCING HIS INTENTIONS; INSTEAD OF CONTINUING R TURN HE THEN REVERSED COURSE/BANK TO FULL 30 DEG L TURN WHICH TOOK US RIGHT INTO THE CELL. HE ALSO HOLDS ALT OF FL330 IN SPITE OF BEING CLRED TO FL310 BEFORE ANY DEVS APPROVED. WHEN I STRONGLY REMINDED HIM OF 31000 FT; HE STATED THAT 'THERE WAS NO ONE ELSE UP HERE IN THE CELL WITH US' AND FURTHERMORE 'HE WAS NOT GOING TO DSND UNTIL CLR OF THE WX.' WE SHORTLY THEREAFTER FLEW OUT OF THE WX AND DSNDED TO FL310; NO TCASII ALERT NOTED. A CLR DECISION BY THE PF AT 15-20 MI FROM THE WX CONFLICT WOULD PROBABLY HAVE PREVENTED ANY PROB.